This paper identifies a system for categorizing
breaking waves based on the a.cgiitude, period and quality of the swells from which the
waves originate. A system is provided to methodically compare and contrast waves based on
size and quality from one day to the next. This is of particular importance when trying to
compare rare, large-swell events which occur only several times a decade.

Currently surf from seasons past are memorialized
through anecdotal stories and the experiences of those who had the opportunity to observe
the conditions. As is common with stories, they are only as good as the memory of the
person telling the story, and like all stories, they change and grow with time. This paper
presents a scientific system to accurately and concisely define a swell's signature at any
point in a swell event.

The Swell Rating System (SRS) was created to
eliminate the ambiguity and uncertainties that currently exist when measuring breaking
waves. The SRS was created from data obtained through a systematic process of recording
and analyzing swell data obtained from buoys and the resultant breaking wave height
observations. A by product of this analysis is the ability to accurately predict the face
height of breaking waves based on corresponding offshore buoy readings, even when the buoy
is located over distances approaching 1000 miles from shore. Given this relationship, it
becomes possible to categorize breaking waves based on the relative size and strength of
the underlying swell.

The purpose of offshore buoy networks around the
world is aimed at warning boaters and beackgoers of impending dangerous marine and surf
conditions. But the focus of these programs, and most published data, is non-specific to
the interests of those who actually utilize breaking waves for pursuit of recreational and
professional purposes, like surfers, body boarders, and the like. To fill this need,
various commercial services have evolved. They utilize observational buoy data in
conjunction with forecast models and satellite imagery to predict and report surf
conditions worldwide. But the products of these services tend to be homogenized to attract
and maintain a large client base, and typically lack sufficient detail and depth required
by those who pursue the forward most fringes of the sport or who are performing research.
This paper is aimed at fulfilling this need.

In the past, the only easily available real-time
tools for provided ocean surface conditions to the public were buoy observations provided
via the National Weather Service (NWS) on local weather radios. More recently, similar
data became available via the Internet. Both these services reported significant sea
heights observed at various buoys on either an hourly or 3-hour basis. Once again,
the purpose of such observations were mainly to warn mariners and beachgoers of dangerous
conditions to reduce loss of life and property. Typically an appropriate marine warning
would be issued if dangerous conditions were present or immanent., including
high surf advisories. Using significant seas height data, the study began correlating
near-shore hourly buoy observations to real-time surf observations at Cocoa Beach Florida,
(and more recently) Half Moon Bay California., and to a much lesser extent, the northern
shore of Oahu. By documenting the results, it became apparent, as was expected, that a
correlation existed.

Clearly, progressively larger waves would be
observed as the size and period of the seas increased. But the objective was to determine
the face height (in feet) of waves breaking on unobstructed beaches given a particular
buoy reading and similar swell characteristics. A baseline table was completed in 1989, in
Florida. It should be noted that buoy observations were not publicly reported until one
year prior to this time. Once acco.cgiished, the table was found to be accurate roughly 50%
of the time. In the instances where the table was not correct, the observed breaking wave
heights were normally less than the height predicted by the table. Subsequent observations
drove updates to the table as understanding of the baseline and buoys evolved, but the
confidence factor could not be improved beyond the 65% factor.

All measurements were taken at a break known as
RCs, in Satellite Beach, Florida and using Buoy 41009, located 20 nmiles east of
Cape Canaveral. By definition, RCs only breaks on swells originating from between 45
- 90 degrees and within approximately 1500 nautical miles (nmiles). It was discovered that
a straight-line percentage factor could be a.cgiied to scale the prediction for
other breaks within the region with a high degree of confidence. (Such methods are
discussed in the section titled Scaling Factors.)

The original study included wave periods ranging
from 8 seconds to 17 seconds. Though not included in the current table, wave periods less
than 13 secs were included early-on because Florida rarely receives legitimate swells
(those which equal or exceed 13 secs), and they are part of the east coast swell riding
experience. It was determined the predictive process defined herein is probably a.cgiicable
to windwaves as well, but since such conditions represent the least treasured end of the
spectrum, research was discontinued.

In 1995, research began at Half Moon Bay,
California using buoy 46012 and a variety of unobstructed breaks in the region. Once
again, a baseline table was established and additional observations were used to verify
the baseline. Because the quantity of swells is much higher in California, the pace of
research rapidly increased. This also coincided with the proliferation of data via the
Internet/World Wide Web. Because Northern California receives many swells in the 14-20
second interval range, and occasionally greater, the upper end of the table was expanded.
A correlation between the Florida based table and the newer California based table was
observed for the data elements they shared.

But a new more dramatic component was also
present. A local break known as Mavericks, was becoming publicly known for its
ability to be board rideable at sizes up to 30 ft. This made Mavericks a contender for the
largest rideable wave in the world, in a class with Waimea Bay (North Oahu) and Todos
Santos (Mexico), and arguably the best of the three. Research at Mavericks permitted the
study to take a broader scope, and focus on waves covering the highest realm of the
rideable spectrum.

Directly measuring the face height of a breaking
wave is an imprecise science. Often the observation is prejudiced by ones viewing
angle, lack of an object to use as a reference point, or personal tendencies to exaggerate
or underestimate. Therefore, the accuracy of measuring a breaking waves height is
only as good as the objectivity of the observer. For this study, all measurements are made
by the author, based on the distance from trough to crest of the wave as it is initially
breaking (commonly known as the peak). The author has over 25 years of experience in wave
measurement. Whenever possible, the measurements were collaborated with other observers of
equal or greater experience at the time of occurrence, or from measuring photographs of
riders and waves taken during measurement events. Whenever a measurement is in
question, it is discarded or the lowest reading within the probable range was utilized.

Buoy measurements are not an exact science
either. Energy frequency data is obtained through a variety of accelerometers contained
within the buoy. Data is transmitted to a satellite network and down-loaded to a central
computer for processing. Readings are taken once every hour for a ten minute interval. The
frequency data is decoded and processed, resulting in an average of the highest one-third
of waves recorded during the sa.cgie period. Initially the National Weather Service only
reported significant seas. Significant seas are defined as the average of the
highest one-third of combined swells and wind waves. In the open ocean, chop and swells
generated from a variety of sources (storms, gales, high pressure systems, and high/low
pressure gradients) interact. The buoys record these conditions, and filtering is a.cgiied
to eliminate erroneous and transitional spikes. The resultant readings are broadcast.

Lately, additional algorithms are being used
which group wave energies by frequency, permitting wind waves and swell (ground swell) to
be separately identified. Observation has determined that the most desired feature
required for producing rideable waves is swell. Locally generated wind waves have an
additive effect on overall height, but significantly degrade quality as the ratio of
windwave to swell increases. It was this interaction of wind wave and ground swell that
caused the relatively low 65% accuracy rate identified previously. With the publication of
ground swell readings from the buoys (i.e. equal to or greater than a period of 13 secs),
the accuracy rate has significantly improved.

Additionally, the University of California (San
Diego) has i.cgiemented another buoy network which identifies predominant direction (in
feet, period and degrees) of both north and south bound swells. This data has been used to
validate NWS provided swell data.

Based on descriptions of how measurement data is
obtained, it is apparent that both the wave face height and buoy measurements have a
probability for variability, error or inaccuracy. Namely, breaking wave face heights are
measured by inference rather than direct scaled means, and swells (as measured by the
buoys) are transcribed through a inferred method. This is not to say an exact correlation
between swell heights and breaking wave height is not possible, but that an appropriate
deviation range has been considered when producing the final results.

This section contains the most recent generation
table of buoy and breaking wave observations. The table groups swells of various periods
and sizes into categories. There are 2 features worthy of note:

The table establishes Swell Categories, based on
their resultant expected breaking wave face height. Much like the Saffir-Simpson and
Fujisaki scales for indicating hurricane and tornado destructive potential, this table is
broken into categories based on traditional size barriers recognized within the wave
riding community.

The table consolidates translation of swell
readings of different periods into one standard set of measures. That is, waves of
different periods, though they contain different levels of total energy, can be grouped
together based on their expected breaking wave face heights.

The horizontal axis identifies standard swell
periods. The vertical axis identifies swell categories. The interior of the table groups
derived swell measurements based on size/a.cgiitude (in feet) and period (in secs)
from the buoys and assigns them to a category. Swells that result in similar sized
breaking wave face heights are grouped together.

The list below identifies parameters within which
the table is a.cgiicable. If any of the parameters are not met, scaling factors should be
a.cgiied to produce a valid measurement. (Note: A.cgiication of scaling factors may degrade
resultant accuracy.)

Beach must be unprotected . Unprotected is defined
as:

No obstacle must be present that creates drag or
refraction of the swell or prevents a swell from arriving at the beach unimpeded. Exa.cgies
of impediments include a point (which causes swell redirection/wrapping), isthmus, island,
shoal, peninsula, or submerged obstacle (including waters less than 90 meters deep within
20 nmiles from shore).

Readings must be from a near-shore buoy.
Near-shore is defined as the buoy being located within 20 nmiles of shore and in
approximately 90 meters of ocean depth. (Note: Buoy 51001 off Kauai , typically used on
the North shore of Oahu, HI does not meet this criteria because it is anchored in a depth
of 3000 meters . Therefore, scaling factors should be a.cgiied. Buoys 46006 and 46059 off
the northern California coast also are in a similar situation.)

The Category Characteristics Table correlates
swell categories to expected breaking wave face height measurements. Several measurement
types are provided to address the variety of scales typically used by various sub-factions
of the wave riding community.

The horizontal axis identifies a category and a
breaking wave face height size measurement using each of the different scales. Each scale
is described below:

Apparent Size: The size of the wave face measured
by comparing it to the size of standing rider (surfer) on that wave. (Assuming a
average rider is about 59" tall and assuming a normal surfing
position, total height would be about 50".

Measurable Size: The actual breaking wave face
height if a photograph of the wave was taken and a standard of measure (in feet) was
a.cgiied to it.

Hawaiian Size Equivalent: A regional scaled
a.cgiied mainly at breaks in Hawaii. This scale measures the back of a breaking wave rather
than its face.

Mavericks (Apparent) Size: Same as apparent size,
only occurring at Mavericks. Most unobstructed sandbar and reef breaks become unrideable
once the swell size is sufficient to start becoming rideable at Mavericks. They become
closed-out. Conversely, when the swell is small enough to be rideable at most sand-bar and
reef breaks, no waves break at Mavericks because the water depth at the reef is too deep
to allow waves to break.

Mavericks Measurable Size: Same as Measurable
Size. Because of the reef at Mavericks, the size is actually magnified (positive scaling)
compared to other breaks experiencing the same swell conditions.

The vertical axis identifies each of the 7 Swell
Categories.

Swell Category Characteristics

Category

Surf Description

Apparent Size

Measured Size(In Ft)

Hawaiian Size Equivalent

Mavericks Apparent Size
**

Mavericks Measurable Size **

0

Very Small

flat to less
than waist high

0 - <2.5 ft

NA

1

Small

waist high to
less than head high

2.5 ft -
<5ft

NA

2

Medium

head high to
less than 2.5 ft overhead

5 - 7.5 ft

NA

3

Large

2.5-4.9 ft
overhead

7 .5- 9.9 ft

NA

4

Big

2-3 TimesOverhead

10 -15 ft

NA

5

Medium Big

3-4 TimesOverhead

15-20 ft

12-15 ft

6

Very Big

4-5 TimesOverhead

20 -25 ft

15-20 ft

7

Huge - Epic

5 Times
Overhead+

25 ft +

20 ft +

**Mavericks data available but
intentionally not included here to protect the break and those that have earned the right
to surf it without a crowd.

It should be understood that the breaking wave
face heights defined above are presented as general guidelines for swell classification
purposes, and can vary depending upon the characteristics of the ocean floor where the
waves break. Some ocean floor configurations may a.cgiify the swells breaking wave
size potential (positive scaling), others reduce it (negative scaling), some become
unrideable above a certain size while other only break when the size becomes extreme. Some
waves break on sandbars, others on reefs, rock shelves, or points. Regardless of the
breaks configuration, the table above has been proven to hold generally accurate if used
according to the limitations established herein.

The previous discussion has been based on the
observance of clean ground swells. If viewed graphically, the swell would ideally be
focused within a narrow a.cgiitude and frequency band range.

The presence of secondary or even tertiary ground
and/or wind swells can have an additive effect of overall breaking wave face height. It is
not the intent of this paper to research and discuss findings related to such an effect,
but merely to state that the presence of wind waves and other ground swells of less
significant size and/or period could cause the size predicted by the tables to be
understated.

It is the interaction of ground and wind swells
that caused a low confidence in early versions of the swell table. Namely, the use of
significant sea heights instead of swell introduces a variable
component which cant be accurately measured at this time.

Also, there are some instances where the buoys
report significant seas with a period of 13 sec or greater, yet also report an identical
wind wave reading and no swell reading.

Significant Seas

Wind Wave

Swell

5.1
ft @ 13 sec

5.1
ft @ 13 sec

0.0
ft @ 0 sec

This phenomenon is still being investigated, but
it is suspected it is caused by a swell that has a marginal 13 sec period, and is actually
spread between 11 to 13 sec., making it qualify more as wind wave than ground swell.

A similar condition exists when a ground swell
and wind swell of nearly equal a.cgiitude converge on a buoy simultaneously. Often the
readings over time will be displayed as follows:

Time

Significant Seas

Wind Waves

Swell

Hour 1

10.6
ft @ 17 sec

10.6
ft @ 17 sec

0.0
ft @ 0 sec

Hour 2

10.2
ft @ 17 sec

9.0
ft @ 7 sec

5.7
ft @ 17 sec

Hour 3

10.6
ft @ 17 sec

10.1
ft @ 17 sec

0.0
ft @ 0 sec

Hour 4

10.2
ft @ 17 sec

9.5
ft @ 7 sec

6.2
ft @ 17 sec

The resulting breaking wave face height will not
correlate well with the significant sea readings (being something less), but will be
greater than the sporadic swell reading. It appears, based on observation, to be a
combination of the two, primarily influenced by the swell, and secondarily a.cgiified by
the wind wave.

Such conditions can be difficult to interpret and
make it difficult to construct an accurate breaking wave face height forecast. And the
resulting breaking waves are less than ideal to ride, commonly called junky or
choppy, even though local winds could be calm. This persistent condition has
resulted in the creation of swell quality criteria. When mult.cgie swells or waves with
periods less than 13 seconds converge at a near-shore buoy, a confidence or Quality factor
has been devised to be broadcast with the Swell Category to indicate the presence of
mult.cgie frequencies occurring simultaneous with the ground swell. A si.cgie 5 point scale
is presented below:

Single (or mult.cgie)
ground swell(s) with one lower frequency (<13 sec) of greater a.cgiitude than the
predominant ground swell and one or more lower energy frequencies of less a.cgiitude than
the predominant ground swell.

2

Single or mult.cgie
ground swells with mult.cgie lower energy frequencies of equal or less a.cgiitude than the
predominant ground swell.

3

Single ground swell
with single secondary frequency in the 11-13 sec period range of equal or less a.cgiitude.

Single ground swell
with no other frequencies present (less than 7% ground swell a.cgiitude).

It is often difficult to determine exactly
which of the above Quality Factors to a.cgiy to a swell without the tools provided
by the National Data Buoy Center via their web site. This site provides graphics
of the various energy frequencies present at each buoy on an hourly basis. The
lower the frequency, the higher the associated energy level, and period. It
appears that energy levels of .5 hertz equate to a period of about 20 seconds.
A si.cgie review of the hourly graphic clearly identifies the presence of one
or mult.cgie frequency levels. The presence of mult.cgie lower frequency swells
occurring simultaneous with a large primary ground swell often makes the primarily
swell unrideable, or at least, less desirable.

Reviewing data at the prime buoy URL
(http:www.nws.fsu.edu/buoy/) for the same time period indicates the presence and a.cgiitude
of both predominant ground swell and lesser energy waves (wind waves).

Swell, wind, secondary swells, wind waves and
tide change hourly and interact on a minute by minute basis to produce the dynamic medium
on which wave riding sports are practiced, and large waves of quality are at best
exceedingly rare and fleeting in nature. This is well understood by the wave riding
population, and large surf of quality is something to be coveted, remembered and
memorialized. It is with this historical background that a system to ensure accurate
comparison is proposed.

Though a swell rating can be computed at any
point during a swell event, the swell signature should be computed at the peak of the
swell event. This is easily determined by reviewing hourly buoy reports over the duration
of the swell event.

The resulting hourly measurements can
be.cgiotted to create a swell profile which maps the evolution of
the swell over its lifespan (See table below). The peak of the swell often
occurs at the point where the swell period transitions from one of its
early high-energy frequencies (typically accompanied by lower a.cgiitudes) to
the next lowest frequency band (usually accompanied by a subsequent increase
in a.cgiitude). The combination of Swell A.cgiitude and Period that result in
the largest Swell Rating define when the Peak is reached.

Once one computes the peak Swell Category, the
corresponding Swell Quality Factor should be determined. Once thats complete, the
Swell Rating can easily be assigned.

The Swell Rating is determined by concatenating
the Swell Category and Swell Quality components. The resulting number defines
the value, or signature for the swell and resultant breaking waves at the time
the observations are taken. This is achieved by first identifying the Swell
Category rating, then the Swell Quality rating. They should be separated with
a decimal point (.). This method is similar to one created for rating
difficulty of rock climbing paths.

Format: XX.YY

Where XX equals the Swell
Category and YY equals the Swell Quality.

For exa.cgie:

If Swell Category rating = 7

And Swell Quality rating = 5

Then the Swell Rating = 7.5,

This would be the best of all possible
conditions.

Like wise

If Swell Category rating = 0

And Swell Quality rating = 1

Then the Swell Rating = 0.1

This would be the worst of all possible
conditions.

This method provides a means of quantifying swell
size, period, and quality in one concise value.

From the exa.cgies above, its now possible
to construct a matrix with 40 degrees of fidelity to describe all possible surf
conditions. The X axis identifies swells in increasing size from left to right, while the
Y axis identifies swells in increasing quality from top to bottom. The worst of all swells
appears in the upper left hand corner of the table, while the best of all swells appears
in the lower right hand corner of the table.

The SRS does not consider swell direction, local
winds, tides, or provide a means to rate how the wave breaks relative to other breaks, ie
hollow, mushy, peeling versus 'sectiony', point break versus beach break. It is well
understood that swell size and quality are the two most important factors for determining
the potential for rideable surf. If those two elements are present, it then becomes
an academic and personal preference issue of finding the best break (location), at the
correcttide, with acceptable wind conditions to cause theswell to reach
its maximum potential from a surf riding perspective. But without sufficient swell,
all other influential elements are insignificant.

This system does not attempt to rank surf riding
breaks (locations) because its purely a matter of personal preference. Each break
has its own set of rules regarding optimal swell direction, tide, local winds etc,
and each person has their own criteria for what is optimal surf based on their wave riding
abilities. But again, such a debate is inconsequential, because there must first be swell.

Many NOAA and CDIP buoys are positioned
sufficiently clear of obstacles which impede the progress and strength of swells. Points,
isthmuss, under sea ledges, continental shelves, islands and the like, can block a
swell or cause it to refract, drag, or otherwise loose energy. This results in a decrease
in either swell period or a.cgiitude and can lead to errors when calculating expected
breaking wave face heights. The actual face height may be less than that predicted from
the Swell Category Table, depending on the magnitude of the obstruction.

Swell size, period and quality are the most
significant factors in determining the potential for surf and are the central elements
used in the Swell Rating System (SRS). With the SRS, it is now possible to record the
occurrence of any swell event in a manner that accurately measures its
size and intensity. Correlating buoy derived swell height measurements with breaking wave
face heights eliminates much of the error, exaggeration and hype associated with the
current method of surf measurement. The SRS is several magnitudes of improvement better
than the current system, but there is still potential for error when affected surf breaks
require the a.cgiication of Scaling Factors. Databases still need to be developed on a
break-by-break basis.

It is with this understanding that this proposal
is submitted for use by the surf riding and forecasting community.